Scientists have discovered living things living in unbelievably hostile environments, from hot thermal vents to a lake buried under Antarctic ice to high-pressure deep ocean trenches. Now we have evidence of living things living in rocks under the bottom of the seas -with no access to sunlight at all.

Persisting in microscopic cracks in the basalt rocks of Earth’s oceanic crust is a complex microbial ecosystem fueled entirely by chemical reactions with rocks and seawater, rather than sunlight or the organic byproducts of light-harvesting terrestrial and aquatic ecosystems.

Such modes of life, technically known as chemosynthetic, are not unprecedented, having also been found deep in mine shafts and around seafloor hydrothermal vents. Never before, though, have they been found on so vast a scale. In pure geographical area, these oceanic crust systems may contain the largest ecosystem on Earth.

“We know that Earth’s oceanic crust accounts for 60 percent of Earth’s surface, and on average is four miles thick,” said geomicrobiologist Mark Lever of Denmark’s Aarhuis University, part of a research team that describes the new systems March 14 in Science.

If what the researchers found resembles what’s found elsewhere below Earth’s oceans, continued Lever, “the largest ecosystem on Earth, by volume, is supported by chemosynthesis.”

This ecosystem is completely separated from all other life on earth, living without oxygen. Read about how they do it at Wired Science. Link